Chemistry: Titrations

Titrations

I found a bottle in the stockroom of my lab about a year ago. When I opened it, I knew from the burning smell that it was a bottle of nitric acid. However, I had absolutely no idea what the concentration of the acid was. Without knowing the concentration of the acid, it would be difficult to find a use for it.

Fortunately, there's a way to solve this problem. As I remembered from way back in Chemical Equations, acid-base reactions occur when an acid and base combine by the following general equation:

• HA + BOH ⇔ BA + H₂O

This sparked the following line of reasoning in my brain:

• Every OH^- I add to this solution will neutralize one of the H⁺ ions.
• If I keep adding base to my nitric acid, it will eventually turn into neutral water with a pH of 7.00.
• If I keep track of how much base I put into the acid, the quantity of acid when the pH is equal to 7.00 will be equal to the amount of base I've added.

When the solution is perfectly neutral (called the "equivalence point"), the number of moles of acid that I started with will be equal to the number of moles of base that I added to make them neutral. As a result, we get the very handy equation:

M_aV_a = M_bV_b

for neutralization reactions at a pH of exactly 7.00. Titration is the process in which neutralization reactions are used to determine the concentration of either an acidic or basic solution.

Here's how I did my experiment:

I placed 175 mL of nitric acid into a beaker and added 1.00 M NaOH solution to it. I found that the solution was completely neutral after I had added 365 mL of sodium hydroxide to the acid.

Using the earlier equation, M₁ = 175 mL, V₁ is unknown, M₂ = 1.00 M, V₂ = 365 mL, we find that:

• (175 mL)V₁ = (1.00 M)(365 mL)
• V₁ = 2.09 M

The nitric acid had a molarity of 2.09 M. Why anybody would make a solution with this molarity, I have no idea, but that's what it was!